This project will develop and validate technology that will provide surgeons with new and powerful means to examine and interact with preoperative patient data -- in a manner that will improve patient safety, increase surgeon confidence, shorten procedure times, and improve outcomes. Our underlying hypothesis is that, by providing surgeons with a high-fidelity interactive simulation environment in which they can visually and physically interact with very realistic patient-specific simulations, that they will be able to plan and then rehearse a patient's procedures with sufficient immersion that performing the actual procedure will feel familiar and can be performed with confidence, precision and improved outcomes. These broad goals will be achieved by accomplishing four underlying aims including 1) the design and development of a visuohaptic workstation (enabling stereo visual and haptic touch interactions with the medical simulations) and creation of advanced haptic rendering algorithms to enable interaction of virtual tools with detailed patient-specific anatomy (derived from volumetric image data), 2) the development methods for photo-realistic rendering of large volumetric datasets acquired from patient-specific clinical imaging (including realistic rendering of translucent bio-materials and wet surfaces) to portray subtle visual cues essential for making surgical decisions, 3) the development methods for real-time, physics-based simulation of interactions between rigid bodies, and deformable tissues (including models and algorithms needed to simulate surgical manipulations such as retraction, incision and resection). In achieving these first three aims we will create a cost-effective visiohaptic workstation for rehearsal by exploiting emerging multi-core and graphics processing units, and high quality graphics and haptic displays, the costs all of which benefit from increasing consumer demand and technical breakthroughs. Finally, our fourth aim will be to assess the accuracy and utility of our patient-specific surgical rehearsal environment for use in cranial-base surgery (focusing on procedures limited to the poster lateral and anterior cranial base) and validate our hypothesis by study of i) subjective "realism" and ease of use, ii) ability to predict exposure of critical anatomy, and iii) its impact on surgical cases.